Electrode gun such as is used in cathode-ray tubes



H. Mos's 2,484,721

ELECTRODE GUN SUCH AS IS USED IN CATHODE-RAY TUBES Oct. 11, 1949.

Filed Jan. 26, 1948 all] ll W:

5 R 1 0 B MM m m NT 1E m Patented Oct. 11, 1949 ELECTRODE GUN SUCH AS ISUSED IN CATHODE-RAY TUBES Hilary Moss, London,

Cossor Limited, Lo company Application January 2.6, 1948, Serial No.

England, assignor to A. C.

ndon, England, a British In Great Britain March 14, 1942 Section 1,Public Law 690, August 8, 1946 Patent expires March 14, 1962 8 Claims.

This invention relates to electron guns such as are used in cathode raytubes for the purpose (if-generating electron beams, and of focussingthem at least mainly by electrostatic fields.

One of the objects of the invention is to produce an exceptionally finecrossover in the electron beam.

In an electron gun according to the invention, the first anode and thecontrol electrode, which serve with the cathode to establish the firstelectron lens, each consist of an apertured disc electrode having a cupportion surrounding the aperture, formed by dishing and disposed convextowards the cathode, and said anode and control electrode are soarranged that the aperture of the anode issituated within th cup portion01' the control electrode.

An object of a preferred form of the invention is to focus the electronbeam into a fine spot on a target such as a fluorescent screen. This maybe effected by employing a single or unipotential lens to produce on thetarget an image of the crossover. Preferably the potential of the firstand last electrodes of this lens is equal to that of the first anode andthereby the introduction of a third lens between the first lens and theunipotential lens is avoided. A direct connection may be made betweensaid electrodes and the first anode, either inside the tube or in anexternal circuit.

The appended drawing shows in Fig. 1 a crosssectional view of anelectron gun structure in a cathode ray tube embodying principles of thepresent invention, while Fig. 2 shows diagrammatically acathode ray tubeembodying a modified form of the invention.

Cathode I is of a conventional type having a flat active surfacedisposed perpendicular to the axis of the gun. Control electrode 2comprises a cup portion 2| convex towards the oathode I. This cup isformed by dishing. In the middle of the bottom of the cup is an aperture22.

The first anode 3 has a cup portion 3| convex towards the cathode, alsoformed by dishing. In the middle of the bottom of this cup is anaperture 32. This aperture 32 lies within the cup portion 2| of controlelectrode 2.

In a specific example of a gun according to the invention, which hasbeen found to operate satisfactorily, the cups 2| and 3| of theelectrodes 2 and 3 are both of part-spherical form and have equal radiiof 3.17 mm. The diameter of the aperture 22 in the control electrode is0.8 mm. and that *of the aperture 3 in the first 2 anode is 1.8 mm. Thedepth of the cup in the control electrode is 2.07 mm. and that of thecup in the first anode is 1.87 mm.

The spacing between the aperture of the control electrode and thecathode surface is 0.3 mm. The spacing between aperture of the firstanode and that of the control electrode is 1.50 mm.

The crossover is formed within the cup of the control electrode and nearthe aperture of the first anode.

The beam diverges from the crossover as it passes into a tubular secondanode 4. A single lens is formed by the electrostatic field betweensecond anode 4, final anode 5 and the decelerating electrode 6; anodes 4and 5 being maintained at equal potential, the highest potential in thegun and preferably equal to that of the first anode 3, while electrode 6is maintained at a lower potential. The arrangement of potentials isindicated generally in Fig. 2 by the sign and number of the polaritymarks adjacent the Various leads.

The electron beam leaves the electron gun through aperture 58 of finalanode 5 and the beam is now in a form convergent towards a fine spot.

It has been found convenient and efiective to work this tube with thefollowing electrode voltages relative to cathode:

Control electrode 2 2 to volts negative First'anode 3 Second anode 4Final anode 5 Decelerating electrode 6--- 270 volts positive 2,000 voltspositive 42 of diameter 1.8 mm. The divergent beam is masked down bythis additional electrode so that electrons do not impinge on thedecelerating electrode 6. Undesirable secondary emission from electrode6 is thus avoided.

In Fig. 2 I have indicated the electron gun structure as being mountedwithin neck portion of cathode ray tube envelope 6| I claim:

1. A cathode ray tube having an electron gun arrangement including acathode for generating a stream of electrons and electrostatic means forfocussing said stream, said electrostatic in including an apertured disccontrol else having a cup portion surrounding the aperture thereof anddisposed with its convex side adjacent said cathode, and

an apertured disc I anode having a cup portion surrounding the aperturetherein and disposed with its convex por= I tion within the cup portionof said control electrode, and means forming .a'i unipotentiail lens forconverging said stream to aifiri'e' spot including succession a tubularsecond anode, an apertured decelerating electrode and an apertured.final anode, said decelerating electrode and final anode beingcup-shaped and having their cupped sides adjacent one another.

2. A cathode ray tube having an electron gun.

arrangement including a cathode for generating a stream of electrons andelectrostatic means for 4 shaped and having their cupped sides adjacentone another, the first and last electrodes of said lens being connectedto said first anode;

5; cathode fay tube Having an electron gun arrangement including acathode for generating a stream of electrons and electrostatic means for'focussing said stream, said electrostatic means including anapertureddisc control electrode having. a cupportion surrounding the aperturethereof and disposed with its convex side adjacent said cathode, and anapertured disc first anode having a; cupportion" surrounding theaperture therein and disposed with its convex portion within the cupportion. of said control electrode, and

means forming a unipotential lens for converging said stream to a finespot including in successiona' tubular second anode, an apertureddecelera-ting' electrode and an apertured final anode,

ces'sion a tubular second anode, an apertured decelerating electrode andan apertured final anode, said decelerating electrode and final anodebeing c'up s'h'a'ped and having their cupped sides adja' cent oneanother, the first and last electrodes of said lens having a potentialapplied thereto equal to that or said first anode.

3. A cathode ray tube having an electron gun arrangement including acathode for generating a stream or electrons and electrostatic means forfdcuss'irigsaid stream, said electrostatic means including an apertureddisc control electrode having a cup portion surrounding the aperturethereof and disposed with its convex side adjacent said cathode, and anapertured disc first anode having a cup portion surrounding the aperturetherein and disposed with its convex portion within the cup portion ofsaid control electrode, and means forming a unipotential lens forconverging said stream to a fine spot including in succession a tubularsecond anode, an apertured decelerating electrode and an aperturedfinial anode, said decelerating electrode and final anode being cup'shaped and having their cupped sides adjacent one another, the first andlast electrodes of said lens liaving a potential applied thereto equalto that of said first anode, the intermediate electrode of saidl en'shaving alower potential applied thereto;

4. A cathode ray tube having an electron gun arrangement including acathode for generating a stream of electrons and electrostatic means forfocus'sing said stream, said electrostatic means including an apertured'disc contra] electrode having a cup portion surrounding the aperturethere:-

cathode, and an apertured disc first anode having a cup pdrtiohsurrounding the aperture therein and disposed with its convex portionwithin the cup portion of said control. electrode, and means forming aunipotentiallens for converging said stream to a fine spot including insuccession a tubular second anode, an apertured decelerating electrodeand an apertured final anode, said decelerating electrode and finalanode being cupor and disposed with its convex side adjacent said saiddecelerating electrode and final anode being cup-shaped and having,their cupped sides adjacent one another, the first and last electrodesof said lens being connected to said first anode, the intermediateelectrode of said lens being connected to a source of potential lowerthan that of said first anode.

6. A cathode ray tube having an electron gun arrangement including acathode for generating a stream of electrons and electrostatic means forfocussi'ng said stream, said -electrostatic means including an apertureddisc control electrode having a cup portion surrounding the aperture'thereof and disposed with its convex side adjacent said cathode, and an,apertured disc first anode having a cup portion surrounding theaperture therein and disposed with, its convex portion within the cupportion of said control electrode, and means forming a unipoten tiallens for converging said stream to a fine spot including in succession atubular second anode, an apertured decelerating electrode and anapertured final anode, said decelerating elec trode and final anodebeing cup-shaped andhaving their cupped sides adjacent one another, andmeans for preventing said stream from impinging on the intermediateelectrode of said lens.

7. A cathode ray tube having an electron gun arrangement including acathode for generating a stream of electrons and electrostatic means forfocussing said stream, said electrostatic means including an apertureddisc control electrode having a cup portion surrounding the aperturethereof and disposed with its convex side adjacent said cathode, and anapertured disc first anode having a cup portion surrounding the aperturetherein and disposed with its convex portion within the cup portion ofsaid control electrode, and means forming a unipotential lens forconverging said stream to. a fine spot including in succession a tubularsecond anode, an apertured decelerating electrode andv an aperturedfinal anode, said decelerating electrode and final anode beingcup-shaped and having their cupped sides adjacent one another, and meansfor preventing said stream from impinging on the intermediate electrodeof said lens, includingan apertured disc electrode following said firstanode and connected to said tubular anode. I

8. A cathode ray tube having an e1ectrcn=gun arrangement including acathode for generat ing a stream of electrons and electrostatic meansfor focussing said stream, said electrostatic means including anapertured disc controlelectrode having a cup portion surrounding tlie 5aperture thereof and disposed with its convex side adjacent saidcathode, and an apertured disc first anode having a cup portionsurrounding the aperture therein and disposed with its convex portionwithin the cup portion of said control electrode, and means forming aunipotential lens for converging said stream to a fine spot including insuccession a tubular second anode, an apertured decelerating electrodeand an apertured final anode, said decelerating electrode and finalanode being cup-shaped and having their cupped sides adjacent oneanother, and means for preventing said stream from impinging on theintermediate electrode of said lens, including an apertured discelectrode following said first anode and having a potential appliedthereto equal to that of said tubular anode.

HILARY MOSS.

REFERENCES CITED The following references are of record in the file ofthis patent:

